The present invention relates to the field of implantable medical devices. More particularly, the present invention relates to cardiac pacing systems that provide a method for preventing atrial fibrillation by rapid pacing intervention.
Tachyarrhythmias are episodes of high-rate cardiac depolarizations. Tachyarrhythmias may occur in one chamber of the heart or may be propagated from one chamber to another. Some tachyarrhythmias are sufficiently high in rate to compromise cardiac output from the chamber(s) affected, leading to loss consciousness or death, in the case of ventricular fibrillation or weakness and dizziness in the case of atrial fibrillation. Atrial fibrillation is often debilitating, due to the loss of atrial cardiac output, and may sometimes lead to ventricular fibrillation.
Generally, fibrillation may be terminated by administering high energy level cardioversion/defibrillation shocks or pulses until the fibrillation is terminated. For example, in the context of implantable anti-arrhythmia devices, these pulses may be applied by means of large surface area electrodes on or in the chamber to be defibrillated. However, the high energy level pulses are often sufficient to cause pain to the patient. Moreover, in some cases an atrial defibrillation pulse is delivered at an inappropriate time and may cause ventricular arrhythmias. Thus, it would be desirable to prevent or decrease the occurrence of atrial fibrillation.
Implantable pulse generators (IPGs) that deliver pacing level pulses are well known in the art. In some cases, patients already having an IPG are the same patients susceptible to atrial fibrillation. It would thus also be desirable to administer preventive measures against atrial fibrillation using the IPGs already implanted in the patient.
Some IPGs are equipped to sense Premature Atrial Contractions (PACs) and/or Premature Ventricular Contractions (PVCs). PACs/PVCs may be used to indicate the onset of a cardiac event such as an atrial fibrillation. It would also be desirable, therefore, to use PACs, PVCs and other xe2x80x9ctriggerxe2x80x9d events that indicate the onset of atrial fibrillation to help prevent or decrease the occurrence of atrial fibrillation.
Thus, a need exists in the medical arts for using cardiac xe2x80x9ctriggerxe2x80x9d events that indicate the onset of atrial fibrillation and rapid pacing intervention to prevent or decrease the occurrence of atrial fibrillation.
Some methods have been proposed in the prior art for the prevention of atrial fibrillation using pacing pulses.
For example, U.S. Pat. No. 5,713,929 to Hess et al. discloses a pacing algorithm which paces the heart at a faster than indicated rate during detection of PACs/PVCs. The algorithm then reduces the pacing rate to a safety rate unless natural depolarizations are detected.
The article xe2x80x9cA New Pacing Algorithm for Overdrive Suppression of Atrial Fibrillationxe2x80x9d by Murgatroyd, et al. in the journal PACE discloses increasing the atrial rate by 12.5% following detection of a PAC. The rate is then decreased by 63 msec until the lower rate is reached or intrinsics are sensed.
The article xe2x80x9cPacing Strategies to Prevent Atrial Fibrillationxe2x80x9d by Fahy, et al. in the journal Cardiology Clinics discloses overdrive pacing to prevent fibrillation.
The publication from Quintech regarding xe2x80x9cQuintech Dynamic Overdrivexe2x80x9d discloses atrioventricular sequential pacing at the upper rate limit after atrial fibrillation has ended.
The most pertinent prior art publications known at the present time are shown in the following table:
Murgatroyd, et al. (November 1994) xe2x80x9cA New Pacing Algorithm for Overdrive Suppression of Atrial Fibrillationxe2x80x9d. PACE, Volume 17, Part II, pp. 1966-1973.
Fahy, et al. (November 1996) xe2x80x9cPacing Strategies to Prevent Atrial Fibrillationxe2x80x9d. Cardiology Clinics. Volume 14, Number 4, pp. 591-596. xe2x80x9cQuintech Dynamic Overdrivexe2x80x9d
The publications listed in Table 1 are hereby incorporated by reference herein, each in its entirety. As those of ordinary skill in the art will appreciate readily upon reading the Summary of the Invention, the Detailed Description of the Preferred Embodiments and the Claims set forth below, at least some of the devices and methods disclosed in the patent of Table 1 may be modified advantageously in accordance with the teachings of the present invention.
The present invention is therefore directed to providing a method and system for preventing atrial fibrillation by pacing at a slightly shorter interval than the PAC coupling interval once a first PAC has been sensed and pacing at an even more aggressive interval once an additional PAC is sensed. The system of the present invention overcomes at least some of the problems, disadvantages and limitations of the prior art described above, and provides a more efficient and accurate means of preventing atrial fibrillation.
The present invention has certain objects. That is, various embodiments of the present invention provide solutions to one or more problems existing in the prior art respecting the pacing of cardiac tissue. Those problems include, without limitation: (a) patients experiencing discomfort from atrial fibrillation; (b) difficulty in administering high energy stimulus pulses to treat atrial fibrillation, (c), difficulty in administering therapy for atrial fibrillation using pacing pulses; (d) difficulty in providing pacing pulses at appropriate intervals to prevent atrial fibrillation; and (e) difficulty in using PACs, PVCs and other cardiac xe2x80x9ctriggerxe2x80x9d events to signal onset of atrial fibrillation.
In comparison to known pacing techniques, various embodiments of the present invention provide one or more of the following advantages: (a) the use of pacing energy level pulses to prevent or decrease the occurrence of atrial fibrillation; (b) the ability to detect the onset of possible atrial fibrillation (c) the ability to adjust pacing intervals for use in prevention of atrial fibrillation, (d) the ability to decrease or prevent the occurrence of atrial fibrillation, (e) the ability to use already-implanted IPGs to administer therapy for atrial fibrillation and (f) fewer patient complaints of discomfort in the treatment of fibrillation.
Some embodiments of the present invention include one or more of the following features: (a) an IPG capable of preventing atrial fibrillation; (b) an IPG capable of sensing potential atrial fibrillation and adjusting pacing intervals to prevent the fibrillation from occurring; (c) methods of preventing atrial fibrillation with pacing energy level pulses rather than high energy shocks and (d) methods of sensing potential atrial fibrillation and adjusting pacing intervals to prevent the fibrillation from occurring.
At least some embodiments of the present invention involve pacing cardiac tissue based on an initial pacing interval. A first fibrillation-indicating event is detected. A first adjusted pacing interval is determined. The cardiac tissue is paced based on the first adjusted pacing interval for a first duration in an attempt to capture the cardiac tissue. If the first adjusted pacing interval does not capture the cardiac tissue, an additional fibrillation-indicating event may have occurred earlier to the first fibrillation-indicating event and may be detected. An additional adjusted pacing interval may then be determined and the tissue paced according to the additional adjusted pacing interval in a further attempt to capture the cardiac tissue.